Our findings confirm that nonunion after a clavicular fracture is an uncommon occurrence, although the prevalence is higher than has been previously reported in retrospective series2,4,10. Our study cohort was a consecutive series of patients who presented to our unit following a clavicular fracture and who were followed prospectively. Other than a small minority of individuals who underwent emergency surgery because of skin compromise or floating shoulder, all patients were initially managed nonoperatively. The broad demographic features of the study group were similar to those identified in previous epidemiological studies2,3,11,12. It is therefore likely that the prevalence of nonunion in our study is representative of the prevalence of this complication among fractures initially treated nonoperatively.
Medial end fractures were comparatively rare, accounting for <5% of all fractures in this series. Estimating the relative importance of risk factors for nonunion, therefore, was difficult, and a detailed statistical analysis was not performed. For the small number of patients in this series who sustained a medial end fracture, the rate of nonunion was relatively high and the risk appeared to be increased for fractures with complete displacement compared with those that had residual cortical apposition; however, because of the small number of patients who sustained a fracture in this location, the difference was not significant.
Diaphyseal fractures were the most common fracture in this series, accounting for nearly 70% of the fractures. The majority of these fractures occurred in a younger, predominantly male population and were often caused by a sports injury or a traffic accident. A high proportion of the fractures sustained in traffic accidents occurred in individuals riding bicycles. Since this population was skewed toward the young, the majority of nonunions were encountered in this age-group. However, paradoxically, the risk of nonunion was highest in elderly female patients with a diaphyseal fracture. Most nonunions in younger individuals require surgical intervention because of the poor function associated with the development of this complication, while some of the more elderly patients may not require surgery because of their reduced functional demands13-15.
We were unable to predict with greater sensitivity the risk of nonunion after a diaphyseal fracture, when taking into account the severity of fracture displacement, as other studies have done1. It is possible that fractures with more displacement are associated with a poorer functional or cosmetic result or with the development of malunion, thoracic outlet syndrome, or other symptoms of brachial plexus irritation16,17, and the risk of these complications and the risk of nonunion may be reduced by performing surgery at an earlier stage. However, at present, most diaphyseal fractures of the clavicle are initially treated nonoperatively, and the most common reason for operative treatment remains nonunion. Therefore, we believe that additional modifications to the existing classification systems2,9 are unnecessary.
Lateral end fractures accounted for approximately one-third of the fractures in this series. The risk of nonunion was highest in elderly patients, and, because a greater number of elderly patients sustained a lateral end fracture, they had a relatively higher proportion of the nonunions than did patients with a diaphyseal fracture. Many patients with a nonunion are relatively asymptomatic, despite the nonunion, and they do not subsequently require surgical intervention2,8.
We developed multivariate models to estimate the risk of nonunion after diaphyseal and lateral end fractures. These models may be used clinically to counsel patients about the risk for the development of this complication immediately after the injury. Although these models can be used to assess the risk of nonunion following a fracture, their positive predictive power is still low, as most fractures have united by twenty-four weeks, irrespective of the number of risk factors for nonunion.
A potential weakness of our study is the relatively high proportion of patients who were lost to follow-up before the final assessment at twenty-four weeks. Many of these patients were frail and demented or had died. However, ninety-five patients who remained locally resident were lost during the twenty-four-week follow-up period, even though they were offered additional follow-up appointments, and forty-nine patients could not be traced. We were unable to confirm whether these fractures had united, and it could be argued that many of these patients probably failed to return for the follow-up examination because they were asymptomatic, with a healed fracture. The possibility exists that we have, therefore, overestimated the risk of nonunion in our series. However, the demographic data for the patients lost to follow-up were not significantly different from those for the remainder of the patients with a clavicular fracture, suggesting that the patients who completed follow-up were representative of the population as a whole. We also think that our use of a survival methodology to analyze our data was the most effective way of reducing the potential for confounding introduced by those lost to follow-up.
It could be argued that a watershed of twenty-four weeks for the diagnosis of nonunion is too late in the management of a patient with a clavicular fracture, and surgery should be considered for the treatment of a nonunion at an earlier stage. However, our results demonstrated that approximately 90% of diaphyseal fractures and 80% of lateral end fractures that are unhealed at twelve weeks will progress to union by twenty-four weeks. There is evidence from the Cox proportional-hazards model that patients with a lower prognostic index have worse prospects for progression to union if the fracture remains ununited at twelve weeks. For instance, a patient with a prognostic index of –2 (for example, a sixty-year-old woman with a displaced, comminuted diaphyseal fracture) has a 72.4% projected probability that the fracture will remain ununited at twelve weeks and a 38.3% probability of nonunion at twenty-four weeks, whereas a patient with a prognostic index of –1 (for example, a twenty-two-year-old man with a displaced but noncomminuted fracture) has a 41.6% probability that the fracture will remain ununited at twelve weeks and only a 7.4% probability of nonunion at twenty-four weeks. This suggests that earlier surgery might be beneficial for patients with a lower prognostic index. However, age is a major determinant of the prognostic index, and the lower functional expectations of the elderly may lead such patients to decline the surgery or it may be deemed to be inappropriate for many of them. It is also unclear whether earlier surgery with its attendant risks of infection, fixation failure, and persistent nonunion would guarantee an improved result compared with the traditional methods of nonoperative treatment in most patients18,19. A prospective, randomized, controlled trial of primary operative treatment compared with nonoperative treatment in stratified high-risk groups would be useful to evaluate this issue further.
Life tables of the clavicular fractures at the various time-intervals are available with the electronic versions of this article, on our web site at www.jbjs.org (go to the article citation and click on “Supplementary Material”) and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM).
In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from Scottish Orthopaedic Research Trust into Trauma (SORT-IT). None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Shoulder Injury Clinic, Orthopaedic Trauma Unit, Edinburgh, Scotland
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